1. Field of the Invention
The present invention relates especially to an antenna system capable of working in several distinct frequency ranges, for example a first frequency band which is a low-frequency band [Fbb, Fbh] covering at least one octave and a second frequency band, which is a high frequency band [Fhb, Fhh], the two bands being separated by a difference such that Fhb greater than =2Fbh.
2. Description of the Prior Art
Broadband antennas capable of working with radio equipment in the VHF (Very High Frequency) band, covering frequencies of 30 to 88 MHz, are known in the prior art.
For example, the U.S. Pat. Nos. 4,496,953 and 4,302,760 describe antennas of this kind. FIG. 1 is an exemplary antenna A installed on a land vehicle V. The antenna is formed essentially by an upper radiating element 1 and a lower radiating element 2, both powered by means of a power supply device 4. A mounting base 5, usually provided with a spring 6 to protect the antenna from accidental impact against obstacles, is used to install this antenna on the vehicle. To provide the vehicle with radioelectrical insulation against the ground of the vehicle, the lower radiating element 2 is normally equipped at its lower end with an RF cable choke 3.
Modern transmitter-receiver (or transceiver) stations, working for example in the 30-88 MHz band, presently have a service channel that implements other frequency bands, especially the UHF (ultra-high frequency) bands in the 2.4-2.5 GHz frequency range. The radiating elements 1 and 2 of the above-mentioned wideband antenna, which have a length sized for the 30-88 MHz VHF band, typically a length of about 1.6 meters, are not appropriate for efficient operation at the 2.4-2.5 GHz UHF frequencies. These frequencies indeed necessitate radiating elements whose size is about thirty times smaller.
For these VHF transmitter-receiver stations having a UHF service channel, the commonly adopted solution lies in providing for an additional antenna Axe2x80x2 dedicated to this UHF channel as shown in FIG. 2a. An exemplary schematic installation diagram of this solution is shown in FIG. 2b which gives a diagrammatic view of a transmitter-receiver station 7 powering a VHF antenna A and a UHF antenna Axe2x80x2 through a duplexer 8 whose role is to separate the VHF frequencies and the UHF frequencies and route them towards their respective antennas.
However, this solution gives rise to requirements of installation that entail very heavy constraints. These are:
the need to have a free location on the vehicle to mount the additional UHF antenna,
the need to obtain heightwise clearance for this additional UHF antenna, which is small-sized, so that it is not masked by other devices of the same vehicle,
the need to have an external duplexer to separate the VHF main channel from the UHF service channel if the transmitter-receiver station has only one output connector for both channels.
The object of the present invention relates to an antenna system making it possible to have a single wideband antenna, simultaneously covering at least two distinct frequency bands, a low-frequency band [Fbb, Fbh] covering at least one octave and a high frequency band [Fhb, Fhh], the two bands being separated by a difference such that Fhb greater than =2Fbh. For example, it is possible to work in the 30-88 MHz VHF band and the 2.4-2.5 GHz UHF band.
The invention relates to a wideband antenna system, capable of radiating or receiving signals in a low-frequency band [Fbb, Fbh] covering more than one octave and a high-frequency band [Fhb, Fhh] with Fhb greater than =2Fbh comprising at least one power supply device powering at least one upper radiating element and at least one lower radiating element, wherein the lower radiating element is provided with at least one antenna assembly adapted to radiating in the high-frequency band [Fhb, Fhh].
The power supply device is connected, for example, to a transmitter-receiver station by means of a transmission line and the lower radiating element is constituted, for example, by a section of the transmission line and the antenna assembly comprises at least one hollow radiating element positioned around the section.
The system may comprises several elements connected to one another and serially by means of line portions, the core of one portion connecting the upper end of the hollow element indexed i to the lower end of the element indexed i+1 and the shielding of the line portion indexed i is connected to the coaxial line, for example to the shielding of the line.
A duplexer is placed, for example, at the lower part of the antenna assembly and is connected to at least one hollow element and to the line section.
The system is used, for example, for RF signals.
The object of the invention has the following advantages in particular:
it removes the need for installing a second antenna for the UHF channel and prevents all the drawbacks that flow from such an antenna, for example bulkiness,
by following certain types of layout, the antenna assembly which contributes to the radiation of the UHF band can be shifted heightwise, thus optimizing the quality of the radio link in this band, which is not the case for the usual installations with a second antenna mounted directly on the roof of the carrier vehicle,
it provides the possibility of making the UHF band with directivity greater than that of a half-wave dipole antenna, making it possible to increase the range of the radio link in this band.